1. Field of the Invention
The present invention relates to an image forming apparatus, a power supply device, and a control method. More particularly, the present invention relates to power control including charge accumulating means.
2. Description of the Related Art
In recent years, according to increasing environmental protection activities, energy saving for image forming apparatuses is demanded. An image forming apparatus including a fixing device of a heat roller system that presses and heats a sheet, a film, and the like having toner images formed thereon consumes a particularly large amount of electric power.
In an image forming apparatus with high image formation speed, to prevent a temperature fall in a fixing roller of a heating unit at the time of an image forming operation, a fixing roller with a large heat capacity may be adopted. In such a case, since a warm-up time as long as several minutes is necessary to raise the temperature of the fixing roller to a usable temperature, a copy waiting time is long. To reduce a heat-up time of the fixing roller, a fixing roller with a reduced heat capacity may be adopted. In such a case, a temperature fall of the fixing roller occurs at the time of the image forming operation. It is possible to solve these problems if the temperature of the fixing roller can be raised quickly by using a 200-volts power supply to increase a power capacity of a heating member such as a halogen heater and increase a transport current. However, as a general commercial power supply for offices in Japan, a power supply with 100 volts and 15 A is used. To adapt the power supply to the voltage at 200 volts, it is necessary to apply special work to a facility in which the power supply is installed. This does not provide a general solution for the problems.
As a method of reducing power consumption of the fixing device on standby, in general, the temperature of the fixing device on standby is kept at fixed temperature slightly lower than a fixing temperature and immediately raised to the usable temperature when the fixing device is used to reduce time for waiting for heat-up of the fixing roller. In this case, even when the fixing device is not used, since a certain degree of power is supplied, energy is consumed unnecessarily. The energy consumption of the fixing device on standby is as high as about 70% to 80% of energy consumption of the apparatus.
As a technology for solving such a problem, in a technology disclosed in Japanese Patent Application Laid-Open No. 2003-297526, an auxiliary heater is provided separately from a fixing heater driven by a commercial power supply and electric power accumulated in a capacitor with a large capacity is supplied to the auxiliary heater to input large power to the fixing heater, reduce a warm-up time of the fixing device, and reduce a temperature change of the fixing device.
In a technology disclosed in Japanese Patent Application Laid-Open No. 2004-266984, a charge accumulating unit (a capacitor) is charged by a voltage supplied from a commercial power supply and electric power is supplied to a load using the voltage charged.
However, in the technology disclosed in Japanese Patent Application Laid-Open No. 2003-297526, temperature detecting units corresponding to a plurality of heaters and a control unit that controls the heaters according to a result of temperature detection by the temperature detecting unit are necessary. This complicates a structure of the fixing device.
In the technology disclosed in Japanese Patent Application Laid-Open No. 2004-266984, it is necessary to use a capacity with a large capacity that charges power at a high voltage. This undesirably increases cost.